Many social scientists have stressed the importance of designing ameliorative social programs so that it is possible to evaluate their effectiveness. As Campbell (1971) and others have pointed out, the major obstacle in getting administrators to take an experimental approach to social reform has been their resistance to use randomization in assigning subjects to treatment and control groups. One focus of the proposed research is to probe factors which may cause administrators, research participants, and the general public to react negatively to randomization. The major thrust of the research, however, is to raise the possibility that random assignment to experimental conditions may itself cause changes in the subjects' attitudes, and motivation that may be mistaken for treatment effects. Subjects who receive a desirable treatment by chance may become excited and enthusiastic; those who miss out on a desirable treatment may become angry and resentful. If so, differences in the experimental and control groups may be caused by reactivity to the randomization process. Some factors likely to affect subject reactivity to randomization have been delineated for the investigation.